What it’s about: Dreaming up possible outer-space habitations always involves thinking big. But no one has thought bigger than theoretical physicist Freeman Dyson, who suggested that humankind a thousand years hence (or a technologically advanced alien race) could build a structure partially or completely enclosing the sun, thereby using most or all of the star’s energy output. Such a structure is called a Dyson sphere, after the man who first imagined it.

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A diagram of a Dyson ring

Strangest fact: There’s more than one type of Dyson sphere. The idea that has caught on in the public imagination, and is most used in science fiction, is that of a Dyson shell—a solid structure completely enclosing the star. But similar concepts have been proposed on less grandiose scales. A Dyson swarm would be a collection of space stations orbiting a star in formation, each collecting energy, either to support an on-board population, or to beam power back to Earth. The simplest Dyson swarm is a Dyson ring, with solar panels arranged in a simple circle around the sun. A Dyson bubble’s components wouldn’t orbit; they would use solar sails, so that the force of the solar wind would perfectly counteract the sun’s gravity, keeping each statite (a stationary satellite) fixed in place.

Biggest controversy: Dyson himself wishes the sphere wasn’t named after him. While the solid sphere enclosing a star completely is the simplest idea to grasp, it’s also the least likely to actually exist. This is partly because not enough material exists in the solar system to actually build such a structure, and partly because a slight shift in gravity could put the sphere off-balance and into a disastrous collision with the sun. While the solid-sphere concept is the one most often attributed to Dyson, he himself has insisted building one is impossible, even with the most advanced technology, and that his concept involved a cloud of objects surrounding the star—basically, any of the related concepts listed above except the one people are most familiar with.

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A possible configuration for a Dyson bubble

Thing we were happiest to learn: We may have recently taken a step toward making one of these concepts an eventual reality. To create the statites neccesary for a Dyson bubble, each component would need a solar sail, made of a material less than one percent the density of paper. The recently invented graphene is thin enough, although we can not yet produce large sheets of the stuff. However, it’s possible that a mesh of another recent invention—carbon nanotubes—could do the trick. The Wikipedia entry suggests that a space station in the style of an O’Neill cylinder, large enough to hold a million people, could be suspended by a sail 3,000 kilometers across—roughly the width of the Atlantic Ocean.

Thing we were unhappiest to learn: So far, we haven’t found any alien Dyson spheres. Theoretically, a civilization far more advanced than ours would be capable of building a Dyson swarm of some sort. This would block their star’s light to the extent that we could detect it. But while SETI has incorporated this idea into its search for alien intelligence, it has yet to bear fruit.

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Also noteworthy: The Dyson-sphere concept can be scaled both up and down. On a smaller scale is a Bubbleworld, in which a solid shell is built around a gas giant (or even a sphere of hydrogen gas). The planet’s thermal energy would power the shell, and people would live either inside the shell or on the surface, as the planet’s gravity would pull people away from the interior. Beyond the Dyson sphere lies the Matrioshka brain, (named for the Russian nesting dolls), a theoretical mega-computer powered by a star at its center. While such a computer is highly theoretical, it’s speculated that a Matrioshka solar system’s inhabitants would simply exist as minds uploaded to a Matrix-style virtual reality.

Best link to elsewhere on Wikipedia: The Dyson sphere is only one of many big ideas conceived by Freeman Dyson. Other concepts the scientist and author created include a genetically engineered tree growing on a comet, capable of sustaining human life; bio-engineered colonies in the Kuiper Belt; searching for life on Jupiter’s moon Europa by seeing if any lifeforms were shot into space and frozen (due to the plumes of water the moon shoots out periodically); and other theories in math and physics too complicated to explain here. Dyson has also been criticized for his views on climate change and nuclear winter—while acknowledging that both exist and are a real threat, he suggests that the science on both is incomplete, and that in both cases these dangers are overblown.